The widespread introduction and acceptance of laser surgical systems in ophthalmic applications ushered in a new era of precision and control. One of the keys to achieving this high level of control is the immobilization of the eye relative to the laser surgical system. In many devices the immobilization is carried out by affixing a patient interface to the objective of the laser surgical system and then docking the patient interface onto the eye. The docking is often achieved by engaging a vacuum suction system. To provide a well-defined optical interface with a known curvature for the optic and the laser beam of the laser surgical system, patient interfaces typically include a contact lens or applanation lens that makes direct contact with the cornea of the imaged eye.
One of the factors the precision and utility of these systems depends on is the patient interface being docked to the eye in a central position. Such a central docking, or centering, aligns an optical axis of the objective of the laser system and an optical axis of the eye. Since the surgical laser beam is typically directed and controlled relative to the optical axis of the objective, aligning the optical axis of the eye with the optical axis of the objective by a central docking can enable controlling and directing the laser beam in the eye with high precision.
Achieving a central docking is often a challenge, though, for multiple reasons. First, the surgical equipment can make maneuvering the objective cumbersome. Also, for some procedures, hard-to-see and hard-to-image structures of the eye, such as their lens, needs to be aligned with the patient interface. Since the lens is often not aligned with the visible structures of the eye, therefore centering the patient interface with a visible structure may result in a misalignment of the patient interface with the lens. Further, the patients sometimes move their eyes during docking, even against their own will, and these involuntary movements need to be compensated by adjusting the patient interface.
To achieve high precision during the alignment and the subsequent docking in face of these difficulties, laser surgical systems often assist the surgeon by including an advanced imaging system. This advanced imaging system can include a stereo microscope, a video monitor and sometimes an Optical Coherence Tomographic (OCT) device. However, integrating these advanced imaging systems into the surgical systems that also use a patient interface can introduce challenges for the system design.